Patent GB-1233465-A (GB)
IPC: G01R5/04
Filed: 1968-08-12
Abstract: 1,233,465. Indicating-apparatus, moving coil meters. ALNOR INSTRUMENT CO. Aug. 12, 1968 [Aug.10, 1967], No.38529/68. Headings G1J; G1Q. In indicating-apparatus with a member 78 which is mounted on a frame 70, 64 by a taut-band suspension and to which a pointer is connected for movement relative to a scale, the suspension includes at least one assembly comprising (a) a hollow piston 140 which is reciprocably mounted in a cylinder 86 fixed to the frame 70 and which has a cap 150; (b) a filament 80 passing through the piston and anchored to the cap 150 and the member 74 and (c) a helical spring 174 round the outside of the cylinder 86 extending between a washer 94 and a shoulder 146 of the piston 140. Applied to a galvanometer, a coil 78 is mounted to swing in the arcuate gap between a soft iron core 74 and the bore 50 in a soft iron central polepiece 46 of a pair of semi-cylindrical magnets by means of two filaments 80, 82 passing through pistons 140, 190 from outer suspension clips 108 to inner anchors 162. The supporting framework comprises a non- ferrous ring 56 on top of the magnets with integral posts 66 to which a bridge part 70 is screwed and webs 62 with a pair of arms 60 depended to support a transverse part 64. The upper metal cylinder 86 has a flange 88 engaging a synthetic resin washer 84 which insulates the bridge 70 from the upper suspension assembly. A zero adjusting lever 92 is mounted above the washer 84 by means of a part 98 with a central bore 100 engaging the cylinder 86, upwardly extending arms 106 straddle the clip 108 and a slotted offset arm 102 is operated by an eccentric screw from outside the housing. The clip 108, preferably formed of beryllium copper which has been spring tempered, has a ring part 110 and an arm 114 with a bend 116 and a radial extension 124, both grooved 130, 128 to seat the filament 80 which is silver-soldered at 120 and connected by a lead 180 to the lever 92. The ring 110 fits over a protrusion 152 of the piston cap 150 with the extension 124 in one of two grooves 154. The anchor 162 of the inner end of the filament 80 is similar to the clip 108, being mounted on a post 164, the legs 166 of which are cemented to the coil 78, a slot 168 providing clearance. A ring 170 secures the anchor 162 and balance arms 172 in place. The clips 108, 162 are formed of relatively heavy gauge metal so that the cantilever extension do not flex. The lower cylinder 86 is not insulated from the part 64 on which it is mounted, thus earthing the coil 78 which is connected to the lower anchor 162 by a lead 184. The lower piston 190 has a separate cap 202 coupled to a head 200, but separated by an antifriction washer 204 preferably of tetrafluorethylene. A holder 220 is clamped to the lower face of the part 64, the cylinder 86 passing through a central hole 222 and, when required e. g. when the galvanometer is part of a pyrometer with a thermocouple whose cold junction is allowed to be at ambient temperature, a clip 228 of phosphor bronze is snapped on to the holder 220. The clip 228 has a finger 232 to which the inner end 236 of a bi-metal compensator 234 is silver soldered, its other end being secured to a link 238 having a pair of fingers 244 for straddling the lower clip 108 for twisting the filament 82 slightly with variation of ambient temperature.